IT WAS SYSTEM TIME.
Delete mac761 from MAME's diff folder (~/.mame/diff) if it preexists. Settings > Runtime: Disable Prevent Writing to Disk. For precautionary reasons the verification input starts at frame 3450. The second part is that it Shuts Down MacOS a little later as well for similar precautionary reasons. roms > mac_hdd > mac761 Add a pre-installed image: mac761.chd SHA1: 3724405a3cbdac97f9fe408e62b1bf4ef20c30b3 SHA256: 39fcfb178f788830c5162827310667a88f83d86b063894a33ca655e8f6e3849c The mac761.dif should be this: SHA1: 0f2af1c5b549f2610f35a05bb90570b1b8aaf7a0 SHA256: f06de5037158f8950a735fb9bb3a88e9c9def7e26a955a1007d0f5ec983857e4 System Time: 799596000